1. Field of the Invention
The present invention relates to a white balance control technology for image data.
2. Description of the Related Art
An imaging apparatus that uses an image sensor such as a digital camera or a digital video camera has a white balance control function of adjusting a color tone of image data acquired by photographing. The white balance control is classified into manual white balance control and automatic white balance control. The manual white balance control is for first imaging a white object to calculate a white balance coefficient, and then applying the calculated white balance coefficient to the entire screen. The automatic white balance control is for automatically detecting a portion likely to be white from the captured image data, calculating a white balance coefficient from an average value among color components of the entire screen, and then applying the calculated white balance coefficient to the entire screen.
In conventional automatic white balance control, when a light source different from that of flash light is present in image data in a flash light emission scene, white balance control is carried out by applying the white balance coefficient calculated as described above to the entire screen. It has, therefore, been difficult to carry out white balance control for achieving appropriate colors for the respective light sources. For example, when a low color temperature light source such as an incandescent light bulb is present as ambient light in the flash light emission scene, flash light is from a high color temperature light source. Thus, when white balance is matched with the flash light, the white balance is not matched with the low color temperature light source. On the other hand, when the white balance is matched with the low color temperature light source, the white balance is not matched with the flash light. Even when white balance control is carried out by setting white balance between both light sources, the white balance is matched with neither of both light sources. Accordingly, a region irradiated with the flash light is bluish, and a region irradiated with light from the low color temperature light source is reddish.
Japanese Patent No. 3540485 discusses the following technology. That is, according to the technology discussed in Japanese Patent No. 3540485, image data captured during flash light emission and image data captured during nonflash light emission are compared with each other for each arbitrary object region to calculate a ratio of the data, and a contribution of the flash light is determined based on a value of the ratio. Then, by selecting a white balance control value for each object region according to the determined contribution, white balance control is carried out.
However, the technology discussed in Japanese Patent No. 3540485 deals with the white balance control when the flash light is emitted. Thus, the technology cannot be applied when no flash light is emitted. Further, development processing is carried out after the white balance control value is varied from one object region to another. This may cause other control operations such as color reproduction to be inappropriate with respect to the white balance control value. Further, no correction is carried out for a human face color. As a result, when a human is present in the image data, the face color may not be appropriate.